Characteristics of saltwater habitat

Saltwater Habitat:

Saltwater habitat is also termed as marine habitat. They include the ocean and seas which accounts for about 97% of earth's water supply. These waters cover about 71% of earth's surface, while also surrounding the continents. Therefore, they separate one continent from another.

Interestingly, the earth has one global ocean. However, they are geographically quite distinct, and may be classified into five. These are:

• Pacific Ocean

• Atlantic Ocean 

• Indian Ocean 

• Antarctic Ocean

• Arctic Ocean 

Please read on the types of aquatic habitat here.

It is noteworthy to state that the waters of the aforementioned oceans could meet at some geographical location. For instance, the pacific and atlantic oceans are the two largest oceans on the planet, covering about half the earth’s surface. Both oceans meet at the Cape Horn.

The diagram below shows five types of oceans surrounding the continents on earth.

You can read on terrestrial habitat here.

Characteristics of Saltwater

The saltwater, marine water, ocean or seawater can best be described through its characteristics. These are explained below:

• 1. Size

The marine water is the largest of all aquatic habitat. It is indeed a vast body of water comprising the seas and oceans. It is worthy of note to state that the terms ocean and sea may be used interchangeably. However, both are not necessarily the same.

The main differences between the ocean and sea is its size and bother with land. An ocean is much larger than the sea; and together, they cover about 71% of the earth's surface. However, the ocean contains less salt than the sea.

Seas refers to the waters situated at the margins of the ocean, and are partly bordered by land. In this regard, you can think of the sea as an extension of the ocean. Therefore, an ocean may have one or more seas.

The volume of of water contained in the ocean is about 1.37 billion km³, and this is equivalent to approximately 97.5% of earth's water. This great amount of oceanic waters cover an area of approximately 361 million km² (or 139 million miles²).

Please read interesting facts for students here.

The table below shows the types of ocean, their region of presence and size.

• 2. Light Intensity 

The intensity of light differs within the ocean and seas. It is highest at the water surface and decreases downwards to about 200 meters (or 660 ft).

The region of light in the ocean is termed epipelagic zone (or sunlight zone). Plants utilizing sunlight energy are present on the epipelagic zone of the ocean.

There is no sunlight energy at the bottom of the ocean. For this reason, nothing really grows there. However, there could be openings in the sea floor, out of which heated mineral-rich water flows. These are termed hydrothermal vents.

The ocean is generally divided into three zones based on the amount of sunlight it receives. These are summarized below:

• Euphotic Zone: This is also termed as  sunlight or epipelagic zone. It runs from the surface of the waters through 200 meters below. Adequate sunlight penetrates this zone; and as a result, photosynthesis occurs here, supporting the growth of plants such as phytoplankton and algae.

• Dysphotic Zone: This is also termed as the twilight or mesopelagic zone. It runs from the bottom of the euphotic zone to about 1005.84 meters below. However, small amount of sunlight reaches this zone, but this is insufficient to bring about photosynthesis. For this reason, photosynthetic plants are not likely to thrive here. Organisms in this zones are dependent on downward drifting plant materials from the sunlight zone, alongside clumps of bacteria, and even some dead animals.

• Aphotic Zone: No sunlight reaches this zone, making plant life absent. Present here are the midnight zone (or bathypelagic zone), with depths between 1,000 and 4,000 meters (3,280 and 13,123 feet). Another region of this oceans's perpetual darkness is termed the abyss (or abyssopelagic zone). It is present between 4,000 and 6,096 meters (1219.2 to 20,000 feet). Beyond the abyssal zone is the hadal zone (or hadopelagic zone). Organisms dwelling here may generate their own light.

Please read on autotrophic nutrition, photosynthesis and chemosynthesis here.

• 3. pH

The letters 'pH' means 'potential of hydrogen'. It is a term indicating the degree of acidity or alkalinity of a solution. At the time of writing this article (November 2023), the ocean pH remained somewhat alkaline at about 8.1. However, ocean acidification is an ongoing process as this may eventually lead to a decrease in the earth's ocean pH.

According to reports, the average pH of the ocean between 1950 and 2020 fell from around 8.15 to 8.05. Apparently, human activities which releases carbon IV oxide (CO₂) are considered the leading cause of ocean acidification.

For ocean acidification to occur, the atmospheric CO₂ dissolves into oceans and seawater, combining with these waters to form carbonic acid (H₂CO₃), a weak acid.

In water, hydrogen trioxocarbonate IV (H₂CO₃) dissociates into hydrogen ions (H⁺) and bicarbonate ions (HCO3^-) respectively.

Please read on the concept of an acid here.

• 4. Salinity

As the name implies, the saltwater (or marine water) contain larger amounts of salt (NaCl) than the freshwater and brackish water. Simply put, they are more saline than other types of aquatic habitat.

Salinity refers to an amount of dissolved salt in a quantity of water. This ratio of salt to water is measured in parts per thousand (ppt).

The average salinity of the marine habitat is about 35 - 37 parts of salt (measured in grams) per 1000 parts of water (1 liter of water). In this regard, the salinity of marine habitat can be simply written as 35ppt - 37ppt.

You can read on salts in chemistry here.

• 5. Waves

The ocean is never still since waves are always present on the surface of its waters. Waves are caused by contact of blowing wind with the surface of a water body. This contact generates energy that moves the ocean water in circular motion.

Waves transmit energy, not water. They are often caused by wind as it blows across the ocean, seas, and rivers.

There is this concept of tidal wave in oceans. They are caused from the effects of gravitational forces between earth and the moon, and between the sun and the moon. They may also be caused from the gravitational pull of the earth alone.

You can read interesting facts on gravity here.

The fluctuations seen on the ocean water level (waves) typically reaches its peak and lows twice daily. The peak (height) of an ocean's' wave could reach as much as 30 meters (100 ft).

• 6. Temperature

The temperature of oceans vary at different depths. The average temperature at the surface of oceans is around 17^oC (62.6^oF). This can become as high as 30^oC in regions near the equator. On the contrary, the ocean surface temperature are lowest near the poles.

At high latitudes, ocean waters receive lesser sunlight, and these occurs at the poles. However, more sunlight is received at the equatorial region (tropics). These variations in sunlight energy therefore implies that the ocean surface can vary from a warm 30^oC (86^oF) in the tropics to a freezing -2^oC to -36^oC(28.4^oF to -96.8^oF) near the poles.

Please read on the concept of heat and temperature here.

• 7. Density

Marine water has a density of about 1.028g/cm³. This high density results for the consequence of its high salt concentration (salinity) and alternating temperatures.

With regards to temperature, lower temperature increases the density of ocean water, even more than higher salinity does.

Since the density of salt is higher in an ocean (compared to those present in other aquatic habitats), we can easily conclude that the ocean water is heavier (or more dense) than other waters, and will sink in them. However, marine organisms can easily float on its waters.

Since the temperature of ocean water decreases as we go down its depth , the density correspondingly increases (as we go down its depths) as well.

Please read more on density here.

• 8. Oxygen Concentration

Marine water have got the greatest concentration of oxygen around its surface. As one goes down the waters, the amount of oxygen decreases accordingly. For this reason, marine divers wear oxygen mask and cannisters when inside its waters.

The shadow zone, or oxygen minimum zone (OMZ) of an ocean refers to the zone where oxygen saturation is lowest. This zone can occur at depths between 200m - 1,500m.

The concentration of dissolved oxygen in ocean water is quite low. It is typically between 7 milligrams and 8 milligrams per liter (7mg/L - 8mg/L).

You can read on Boyle's law here.

• 9. Water Currents

Currents are seen on the surface of marine waters. These currents are caused by the actions of wind over the water. However, currents are also present below the surface of the ocean; and are said to be caused by changes in temperature, pressure and concentration.

Please read Le Chatelier's principal on concentration, temperature and pressure here.

The atmospheric pressure of marine habitat increases down its depth. It is believed that the pressure within the water increases by one atmosphere for every 10.06 meters (33 ft) depth within the ocean and sea. This pressure reaches around 1000 atmosphere beneath the ocean.